This invention relates to injection means for periodically injecting fuel into the combustion zone of an internal combustion engine. In particular, the invention relates to such injection means for dual phase fuel injection in a diesel engine wherein the fuel injection is correlated to engine load and speed.
Conventionally, in order to provide an optimal rate of fuel injection at high engine speeds and loads, a large injector orifice is required. Unfortunately, an orifice sufficiently large to provide high fuel injection rates when required cannot ordinarily provide the fuel atomization necessary during injection at low engine loads and speeds. As a result, at the lower engine loads and speeds fuel is incompletely burned and engine smoking difficulties are experienced. Also, under engine starting conditions, a finely atomized fuel spray is required. It is, therefore, usual for fuel injectors of the fixed-orifice type to have an orifice designed as a compromise between high and low engine load conditions to allow satisfactory engine operation in the major portion of the operating range. As is frequently the case with compromises, the results have not been completely satisfactory. Typically, engine performance at the extremes of the operating range has suffered from insufficiently high fuel injection rates at high load, high speed conditions and insufficient atomization at low load, low speed conditions.
Accumulator-type valves have been employed, particularly with engines having a high output, to obtain greater rates of fuel injection and shorter injection durations. Such accumulator-type injection means typically include a chamber in which fuel is trapped under pressure and then injected into the combustion zones of the engine at the desired time. By this means, very high rates of fuel injection with relatively short injection durations are obtainable. Such accumulator injection means are described, for example, in U.S. Pat. No. 2,985,378 to Falberg. Such accumulator-type injection means, however, are characterized by a high rate of injection at all engine speeds which rate is only minimally reduced as engine load is decreased. Excessive knock and peak cylinder pressure thereby result at low engine speeds. Additionally, the rate of injection is generally too high for optimum engine performance at low speeds.
It is, therefore, desirable to provide injection means utilizable for achieving varying fuel injection rates to provide optimum fuel injection for superior engine performance across the entire normal range of engine operating conditions.